We are attempting to define the genetic basis of cell-cell recognition. As a first step, we plan to characterize the genes encoding the major histocopatibility antigens (transplantation antigens) and the Ia antigens (immune associated antigens by the use of recombinant DNA technology. Our initial efforts have been directed towards obtaining cloned DNAs corresponding to these genes. During the past year we obtained a cDNA clone for the murine Beta2-microglobulin gene and the multiple H-2-like genes are being studied with the aid of the cloned cDNAs.